But we haven’t forgotten the main Medieval: Total WarTM game. The expansion pack also includes:
  • Three new playable factions - the Aragonese, the Sicilians and the Hungarians.
  • New units for many factions, including elite Arabic Faris cavalrymen, Russian Druhzina Cavalry, Hungary Jobbagy Infantry, and the fearsome, amazing Organ Gun - a Medieval “machine gun” of sorts!
  • A new pre-battle system that allows you to scout out enemy forces and organise your reinforcements before a battle.
  • Boiling oil in sieges! Beware of sending your men to attack the castle gates!
  • Tweaks, changes and improvements to gameplay, including a couple of new buildings on the technology tree!
  • A brand new Viking Era campaign with a completely new map of the British Isles and Scandinavia.
  • 8 new Viking Era factions, including the Saxons, Welsh, Mercians, Northumbrians, Scots, Picts, Irish - and not forgetting the Vikings!
  • A new Viking Era technology tree - including Drinking Halls, Sacrificial Shrines, a Warrior Hold and a few surprises.
  • New Viking Era military forces, including Huscarles, Saxon Fyrdmen, Viking Thralls, extremely scary and shield-bitingly fearsome Berserkers - and more!
That's from the website. I'd need to be on my own pc to give a better list.
Hmm, the main advantage to upgrading to VI is that you get to play the various mods created as the vast majority are for 2.01. Some that I've tried are MTW XL, BKBs Supermod, Napoleonic TW, and Hellenic TW. They're all quite enjoyable if you ever get bored with the release version.